/usr/share/doc/m4-doc/Dnl.html

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<!-- 
This manual (31 December 2016) is for GNU M4 (version
1.4.18), a package containing an implementation of the m4 macro
language.

Copyright (C) 1989-1994, 2004-2014, 2016 Free Software
Foundation, Inc.

Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License,
Version 1.3 or any later version published by the Free Software
Foundation; with no Invariant Sections, no Front-Cover Texts, and no
Back-Cover Texts.  A copy of the license is included in the section
entitled "GNU Free Documentation License." -->
<!-- Created by GNU Texinfo 6.3, http://www.gnu.org/software/texinfo/ -->
<head>
<title>GNU M4 1.4.18 macro processor: Dnl</title>

<meta name="description" content="GNU M4 1.4.18 macro processor: Dnl">
<meta name="keywords" content="GNU M4 1.4.18 macro processor: Dnl">
<meta name="resource-type" content="document">
<meta name="distribution" content="global">
<meta name="Generator" content="makeinfo">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<link href="index.html#Top" rel="start" title="Top">
<link href="Indices.html#Indices" rel="index" title="Indices">
<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
<link href="Input-Control.html#Input-Control" rel="up" title="Input Control">
<link href="Changequote.html#Changequote" rel="next" title="Changequote">
<link href="Input-Control.html#Input-Control" rel="prev" title="Input Control">
<style type="text/css">
<!--
a.summary-letter {text-decoration: none}
blockquote.indentedblock {margin-right: 0em}
blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
blockquote.smallquotation {font-size: smaller}
div.display {margin-left: 3.2em}
div.example {margin-left: 3.2em}
div.lisp {margin-left: 3.2em}
div.smalldisplay {margin-left: 3.2em}
div.smallexample {margin-left: 3.2em}
div.smalllisp {margin-left: 3.2em}
kbd {font-style: oblique}
pre.display {font-family: inherit}
pre.format {font-family: inherit}
pre.menu-comment {font-family: serif}
pre.menu-preformatted {font-family: serif}
pre.smalldisplay {font-family: inherit; font-size: smaller}
pre.smallexample {font-size: smaller}
pre.smallformat {font-family: inherit; font-size: smaller}
pre.smalllisp {font-size: smaller}
span.nolinebreak {white-space: nowrap}
span.roman {font-family: initial; font-weight: normal}
span.sansserif {font-family: sans-serif; font-weight: normal}
ul.no-bullet {list-style: none}
-->
</style>


</head>

<body lang="en">
<a name="Dnl"></a>
<div class="header">
<p>
Next: <a href="Changequote.html#Changequote" accesskey="n" rel="next">Changequote</a>, Up: <a href="Input-Control.html#Input-Control" accesskey="u" rel="up">Input Control</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Indices.html#Indices" title="Index" rel="index">Index</a>]</p>
</div>
<hr>
<a name="Deleting-whitespace-in-input"></a>
<h3 class="section">8.1 Deleting whitespace in input</h3>

<a name="index-deleting-whitespace-in-input"></a>
<a name="index-discarding-input-1"></a>
<a name="index-input_002c-discarding-1"></a>
<p>The builtin <code>dnl</code> stands for &ldquo;Discard to Next Line&rdquo;:
</p>
<dl>
<dt><a name="index-dnl"></a>Builtin: <strong>dnl</strong></dt>
<dd><p>All characters, up to and including the next newline, are discarded
without performing any macro expansion.  A warning is issued if the end
of the file is encountered without a newline.
</p>
<p>The expansion of <code>dnl</code> is void.
</p></dd></dl>

<p>It is often used in connection with <code>define</code>, to remove the
newline that follows the call to <code>define</code>.  Thus
</p>
<div class="example">
<pre class="example">define(`foo', `Macro `foo'.')dnl A very simple macro, indeed.
foo
&rArr;Macro foo.
</pre></div>

<p>The input up to and including the next newline is discarded, as opposed
to the way comments are treated (see <a href="Comments.html#Comments">Comments</a>).
</p>
<p>Usually, <code>dnl</code> is immediately followed by an end of line or some
other whitespace.  GNU <code>m4</code> will produce a warning diagnostic if
<code>dnl</code> is followed by an open parenthesis.  In this case, <code>dnl</code>
will collect and process all arguments, looking for a matching close
parenthesis.  All predictable side effects resulting from this
collection will take place.  <code>dnl</code> will return no output.  The
input following the matching close parenthesis up to and including the
next newline, on whatever line containing it, will still be discarded.
</p>
<div class="example">
<pre class="example">dnl(`args are ignored, but side effects occur',
define(`foo', `like this')) while this text is ignored: undefine(`foo')
error&rarr;m4:stdin:1: Warning: excess arguments to builtin `dnl' ignored
See how `foo' was defined, foo?
&rArr;See how foo was defined, like this?
</pre></div>

<p>If the end of file is encountered without a newline character, a
warning is issued and dnl stops consuming input.
</p>
<div class="example">
<pre class="example">m4wrap(`m4wrap(`2 hi
')0 hi dnl 1 hi')
&rArr;
define(`hi', `HI')
&rArr;
^D
error&rarr;m4:stdin:1: Warning: end of file treated as newline
&rArr;0 HI 2 HI
</pre></div>

<hr>
<div class="header">
<p>
Next: <a href="Changequote.html#Changequote" accesskey="n" rel="next">Changequote</a>, Up: <a href="Input-Control.html#Input-Control" accesskey="u" rel="up">Input Control</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Indices.html#Indices" title="Index" rel="index">Index</a>]</p>
</div>



</body>
</html>
m4-doc 1.4.18-1 / usr / share / doc / m4-doc / Dnl.html
